CN1942947B - Objective optical system, optical pickup device, and optical information recording and reproducing device - Google Patents

Abstract

An objective optical system by which spherical aberration correction necessary for achieving compatibility among a high density optical disc, DVD and CD can be well performed without sacrificing characteristics, such as wavelength dependency of spherical aberration and tracking characteristic, and an optical pickup device and optical information recording/reproducing device using such objective optical system are provided. The objective optical system (OL) is provided for the optical pickup device (PU), which reproduces and/or records information from/in first to third optical information recording medium having a protection layer with a thickness of t1-t3 by using first to third luminous fluxes of a first wavelength (lambada 1) to a third wavelength (lambada 3) emitted from a first light source (LD1) to a third light source (LD3). The objective optical system (OL) is provided with a first diffraction structure (DOE1) whose diffraction order where the diffraction efficiency is maximum is the same for any of the first to the third luminous fluxes; and a second diffraction structure (DOE2) which diffracts the second luminous flux but not the first luminous flux nor the third luminous flux.

Description

Objective optical system, optical pickup device, and optical information recording and reproducing device

technical field

The invention relates to an objective optical system, an optical pick-up device and an optical information recording and reproducing device.

Background technique

In recent years, high-density optical information recording media (also known as optical discs) that have increased recording density by using a blue-violet laser light source have been put into practical use, but for the purpose of simplifying the structure of the optical pickup device, reducing costs and realizing compactness, it is necessary for high-density Compact discs, DVDs, and CDs have interchangeable objective optics.

Patent Document 1 discloses an objective optical system used in an optical pickup device compatible with these three types of optical information recording media.

Patent Document 1: JP-A-2004-265573

The objective optical system disclosed in Numerical Example 2 of the above-mentioned Patent Document 1 has a diffraction structure that produces 2nd order diffracted light for the blue-violet laser beam and 1st order for the red laser beam for DVD and the infrared laser beam for CD. The sub-diffraction light corrects the spherical aberration caused by the difference in the thickness of the protective layer between the high-density optical information recording medium and the DVD through the diffraction action of such a diffraction structure. In addition, when recording/reproducing the information of the CD, by using The divergent light beam enters the objective optical system to correct the spherical aberration caused by the difference in the thickness of the protective layer of the high-density optical information recording medium and CD.

However, this objective optical system has the following two problems. One is that the wavelength dependence of the spherical aberration generated by the diffractive structure may be large. In such a case, a laser light source whose oscillation wavelength deviates from the design wavelength cannot be used, and a laser light source must be selected, which increases the manufacturing cost of the optical pickup device. Since the spherical aberration is proportional to the fourth power of the numerical aperture, the influence of the wavelength dependence of the spherical aberration of the diffractive structure is great in Blu-ray Disc (Blu-ray Disc, BD) using an objective optical system with a numerical aperture of 0.85. Another problem is that when recording/reproducing information on a CD, because the divergence of the infrared laser beam is too strong and the coma aberration of the objective optical system is too large when the track is tracked, it is sometimes impossible to obtain the information for the CD. Good recording/reproducing characteristics.

The diffraction angle of diffracted light is represented by "order of diffraction x wavelength/diffraction pitch". In order to achieve compatibility between optical information recording media using different wavelengths by using diffraction action, it is necessary to have a predetermined difference in the diffraction angle between the wavelengths used. Either of the above-mentioned two problems causes the use of a diffraction structure in which the value of "diffraction order x wavelength" is substantially the same between the wavelengths used for the respective optical information recording media.

In the numerical embodiment 2 of the above-mentioned patent document 1, because the ratio of "diffraction times×wavelength" of the blue-violet laser beam and the red laser beam is 810/650=1.25, which is close to 1 (wherein the unit of wavelength is nm), Therefore, in order to obtain the difference in diffraction angle required to correct the spherical aberration caused by the difference in the thickness of the protective layer of the high-density optical information recording medium and DVD, the diffraction pitch must be small. Therefore, the wavelength dependence of the spherical aberration of the diffractive structure becomes large, and the "problem of selecting a laser light source" becomes apparent as described above. In addition, since the difficulty of mold processing of the diffractive structure also increases, it becomes difficult to form a diffractive structure with excellent precision.

On the other hand, because the ratio of "diffraction times × wavelength" of the blue-violet laser beam and the infrared laser beam is 810/780=1.03, the diffraction angles of the blue-violet laser beam and the infrared laser beam become approximately the same, so it cannot be corrected by diffraction Spherical aberration caused by the difference in the thickness of the protective layer between high-density optical discs and CDs. Therefore, in order to correct the spherical aberration caused by the difference in the thickness of the protective layer between the high-density optical information recording medium and the CD, it is necessary to change the magnification when using the high-density optical information recording medium and when using the CD. As a result, as described above, the "tracking characteristic problem" becomes apparent.

Contents of the invention

The present invention is made in view of the above-mentioned problems, and its object is to provide various characteristics such as the wavelength dependence of spherical aberration or track tracking characteristics, and to realize compatibility between high-density optical discs, DVDs, and CDs, and to provide a good performance. An objective optical system for necessary spherical aberration correction, an optical pickup device using the objective optical system, and an optical information recording and reproducing device equipped with the optical pickup device.

In order to solve the above-mentioned problems, the preferred first form is an objective optical system used in an optical pickup device that uses the first optical information recording medium emitted from the first light source for the first optical information recording medium having a protective layer of thickness t1. A first beam of wavelength λ1 is used to reproduce and/or record information, and for a second optical information recording medium with a protective layer of thickness t2 (t1≤t2), use a second wavelength λ2 (1.5× λ1<λ2<1.7×λ1) second light beam to reproduce and/or record information, for the third optical information recording medium with a protective layer of thickness t3 (t2<t3), use the second light beam emitted from the third light source The third light beam with a wavelength of λ3 (1.9×λ1<λ3<2.1×λ1) reproduces and/or records information, and it is characterized in that the objective optical system has a first diffraction structure and a second diffraction structure, and the first The order of diffraction at which the diffraction efficiency of the diffraction structure becomes the maximum is the same order for any of the first light beam to the third light beam, and the second diffraction structure does not diffract the first light beam and the third light beam , so that the second light beam is diffracted.

The first diffractive structure can correct the spherical aberration caused by the different thicknesses of the protective layers of different optical information recording media. For example, as a method for correcting the difference in thickness of the protective layer of the first optical information recording medium (such as a high-density optical information recording medium) and the third optical information recording medium (such as a CD) using a wavelength ratio of approximately 1:2 The spherical aberration of the first diffraction structure, such as the use of diffraction efficiency to become the maximum diffraction order for any one of the first beam to the third beam of the diffraction structure is the same order, then the first beam (such as blue-violet laser beam) and The ratio of "order of diffraction x wavelength" of the third beam (for example, infrared laser beam) is the value farthest from 1, and the difference in diffraction angle between the first beam and the third beam can be sufficiently large. As a result, the spherical aberration caused by the different thicknesses of the protective layers of the first optical information recording medium and the third optical information recording medium can be corrected by the diffraction effect of the first diffraction structure, because the objective lens optics when using the third optical information recording medium Since the magnification of the system is reduced, the tracking characteristics can be improved. In addition, since a relatively large annular zone pitch can be corrected, a diffractive structure with excellent precision can be formed.

Furthermore, the second diffractive structure can correct spherical aberration caused by the difference in the thickness of the protective layer of different optical information recording media and/or the spherical aberration caused by the difference in the wavelength used. For example, as a method for correcting the spherical aberration caused by the difference in the thickness of the protective layer of the first optical information recording medium and the second optical information recording medium (such as DVD) or due to the difference between the first optical information recording medium and the second optical information recording medium The second diffraction structure using spherical aberration caused by different wavelengths, such as using a diffraction structure that does not diffract the first beam and the third beam, but diffracts the second beam (such as a red laser beam), because the diffraction of the first beam Since the order is zero, the difference in the value of "order of diffraction×wavelength" between the first light beam and the second light beam can be maximized. As a result, the diffraction pitch of the second diffraction structure can be made sufficiently large, and the wavelength dependence of spherical aberration can be improved. In addition, the "non-diffraction" mentioned here means that among the beams passing through the diffractive structure, the luminous flux of the 0-order light is the largest compared with the luminous flux of any other diffracted light.

In addition, as a high-density optical information recording medium (high-density optical disc) in this specification, of course, it includes Blu-ray Disc (BD) or HD DVD (HD), and also includes optical discs, which have a thickness of several to several tens on the information recording surface. An optical disc with a protective film of about nm, a protective layer or an optical disc with a protective film thickness of zero. In this manual, DVD is a general term for DVD series discs such as DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD+R, and DVD+RW. CD, CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW and other CD series of discs in general.

In addition, in this specification, the so-called "objective optical system" refers to an optical system that is arranged at a position facing the optical information recording medium in the optical pickup device, and has the ability to condense the light beam emitted from the light source on the information recording surface of the optical information recording medium. The function of the optical system is movable by the transmission device at least in the direction of the optical axis. In this specification, the so-called "objective optical system" may be a single lens, or consist of one lens group, or may consist of two or more than two lens groups.

A preferred second aspect is the objective optical system according to the first aspect, wherein the same degree is 1, and the flare wavelength λB of the first diffractive structure satisfies the following formula.

λ1<λB<λ3 (1)

From the viewpoint of diffraction efficiency, it is preferable that the diffraction order of the diffracted light that occurs by the first diffraction structure is 1 for any light beam, and optimize (also known as blazed) with the wavelength between the first wavelength λ1 and the third wavelength λ3 actinic). According to the specifications of the optical pickup device equipped with the objective optical system of the present invention, the diffraction efficiency of each wavelength can be appropriately changed by changing the flare wavelength λB of the first diffraction structure within the range satisfying the formula (1). For example, when the specification of the diffraction efficiency of the first light beam is more important than that of the third light beam, it is preferable to set the flare wavelength λB closer to the first wavelength λ1. On the other hand, when the specification of the diffraction efficiency of the second beam or the third beam is more important than that of the first beam, it is preferable to set the flare wavelength λB closer to the third wavelength λ3. In this specification, the "flare wavelength λB" refers to a wavelength at which the theoretical value of diffraction efficiency becomes 100%.

A preferred third form is the objective optical system of the second form, characterized in that the numerical aperture of the objective optical system is set to NA1, when the numerical aperture of the objective optical system is set to NA3 (NA1>NA3) when the third optical information recording medium is used to reproduce and/or record information, the flare of the first diffraction structure The wavelength λB, the numerical aperture NA1 and the numerical aperture NA3 satisfy the following expressions (2) and (3).

1.25×λ1<λB<0.95×λ2 (2)

NA3/NA1＜0.7 (3)

In the case that the numerical aperture NA3 of the objective optical system is very small for the numerical aperture NA1 (that is, the numerical aperture NA1 and the numerical aperture NA3 satisfy the situation of (3) formula), it is preferable to form the first in the area corresponding to the numerical aperture NA3. diffractive structure. Thus, since the area ratio of the region (corresponding to the region within the numerical aperture NA3) that occupies the effective diameter of the first wavelength λ1 and forms the first diffraction structure becomes small, even if the diffraction efficiency at the third wavelength λ3 is high In this case (that is, when the flare wavelength λB satisfies the formula (2)), the area-weighted average value within the effective diameter of the diffraction efficiency of the first wavelength λ1 can also be ensured to a very high level. If the flare wavelength λB is larger than the lower limit of the (2) formula, then because the diffraction efficiency of the second wavelength λ2 and the third wavelength λ3 can be ensured very high, the second optical information recording medium or the third optical information recording medium can be made The recording and reproduction characteristics are better. On the other hand, if flare wavelength λ B is smaller than the upper limit of (2) formula, then because the effective diameter inner area weighted average of the diffraction efficiency of the first wavelength λ 1 can be made very high, so can make to the first optical information recording medium Recording and reproduction characteristics are better.

A preferred fourth form is the objective optical system of any one of the first form to the third form, characterized in that the diffraction power of the first diffractive structure is negative.

By making the diffractive power of the first diffractive structure negative, the distance (operating distance) between the objective optical system and the protective layer can be sufficiently ensured when the third optical information recording medium having a thick protective layer is used. In addition, if the diffractive power is negative, there can be a bending point on the optical path difference function (an amount expressed as a function of the height from the optical axis to the amount of optical path difference added due to the diffractive structure). If the optical path difference function has a bending point, since the inclination of the optical path difference function becomes smaller, the annular zone pitch can be widened, and the shape accuracy of the first diffraction structure can be improved. In addition, the term that the diffractive ability is negative or positive means that when the diffractive structure is provided on the flat optical element, the diffractive ability of the flat optical element provided with the diffractive structure is negative or positive.

A preferred fifth form is the objective optical system of any one of the first form to the fourth form, characterized in that the cross-sectional shape of the first diffractive structure including the optical axis is stepped.

If the first diffractive structure has a stepped cross-sectional shape including the optical axis, mold processing can be easily performed, and the shape accuracy of the first diffractive structure can be improved.

The preferred sixth form is the objective optical system of any one of the first form to the fifth form, characterized in that the second diffractive structure is arranged in concentric circles by making the cross-sectional shape including the optical axis into a stepped figure 1. A structure in which a step is only moved by the height corresponding to the number of steps corresponding to the number of steps for each specified number of steps. Through a step difference in the graph, the additional optical path difference for the first light beam becomes the An even multiple of the first wavelength λ1. In addition, the so-called step surface in this specification refers to the surface perpendicular to the optical axis among the surfaces forming a stepped shape, and it is assumed that the highest step surface and the lowest step surface are included when counting the number of step faces. For example, in the case of the form shown in FIG. 13 , the number of rank planes is three. In addition, the so-called one level difference in the graph refers to dp in FIG. 13, for example.

As a structure for obtaining a wavelength-selective diffraction structure that diffracts only the second light beam, the second diffraction structure is made such that the cross-sectional shape including the optical axis is arranged in a stepped pattern in concentric circles For each specified number of order planes, the order is only moved by the height of the order number corresponding to the order number of planes, and a step difference in the graph can also be converted into an even number of the first wavelength λ1 by optical path difference times.

The preferred 7th form is the objective lens optical system of the 6th form, it is characterized in that, through a step difference (adjacent step plane and the step difference between the step planes) in the figure, the additional light for the first light beam The path difference is 1.9 to 2.1 times, preferably 2 times, the first wavelength λ1, and the prescribed number of stages is any one of 4, 5, or 6.

In the second diffractive structure, if a step difference in the figure is converted into 2 times or about 2 times of the first wavelength λ1 by converting the optical path difference, the number of specified step planes formed in a figure is taken as 4, 5, 6, the diffraction efficiency of the second light beam can be ensured higher. In order to maximize the diffraction efficiency of the second light beam, it is preferable to set the number of step planes to five.

A preferred eighth aspect is the objective optical system of the fourth aspect, wherein the numerical aperture of the objective optical system is set to NA1. When the numerical aperture of the objective optical system is set to NA3 (NA1>NA3) when the third optical information recording medium is used for reproducing and/or recording information, the first diffraction structure is formed at a corresponding In the area within the numerical aperture NA3, the objective optical system has the function of not diffracting the first light beam and the second light beam in the area outside the numerical aperture NA3, but diffracting the A third diffractive structure for the third light beam.

The eighth form relates to aperture limitation for the third light beam. For ensuring the action distance when the 3rd optical information recording medium is used, if the diffraction power of the first diffractive structure is set as negative, make its absolute value large, then pass through the convergence of the 3rd light beam in the area corresponding to the inner side of numerical aperture NA3. The light position L1, as shown in the longitudinal spherical aberration diagram of FIG. Between the condensing positions L3 of the third light beam at the outermost periphery E2 of the outer region. In this state, as shown schematically in FIG. 2 , on the information recording surface of the third optical information recording medium, the condensing point of the third light beam passing through the area corresponding to the inside of the numerical aperture NA3 is covered by a The speckle component in the area outside the numerical aperture NA3 may affect the recording and reproduction characteristics. By forming a wavelength-selective third diffraction structure that diffracts only the third light beam in an area outside the numerical aperture NA3, it is possible to separate the focus of the third light beam without exerting an influence on the light-condensing characteristics of the first light beam and the second light beam. Spot and spot components. As a result, the objective optical system can be provided with an aperture limiting function for the third light beam, and recording and reproduction characteristics can be further improved.

The preferred ninth form is the objective optical system of the eighth form, characterized in that, the third diffractive structure is a binary structure of binary value, and the optical path difference added to the first light beam through the step difference of the binary structure is 4.8 to 5.2 times, preferably 5 times, the first wavelength λ1.

If the third diffraction structure is made into a binary structure of binary value, and a step difference is converted into 5 times or about 5 times of the first wavelength λ1 by using the optical path difference, then the additional optical path of the second light beam due to the step difference Since the difference is three times or approximately three times the second wavelength λ2, the first light beam and the third light beam are hardly subjected to the effect of diffraction, and are transmitted almost unchanged. On the other hand, since the optical path difference added by the step difference to the third light beam becomes 2.5 times or about 2.5 times of the third wavelength λ3, the incident third light beam distributes most of the luminous flux to the ±1st order diffracted light, which can give the first The three-diffraction structure imparts a wavelength-selective characteristic of diffracting only the third light beam. Using this third diffraction structure, a specific example in which an objective optical system has an aperture limiting function for a third light beam will be described. In this example, by forming the third diffractive structure in a part of the area corresponding to the outside of the numerical aperture NA3, the annular zone pitch of the third diffractive structure is optimized, as shown in Figure 3 and Figure 4, the third light beam can be separated The spotlight and spot components of .

The preferred tenth form is any one of the objective lens optical system in the first form to the ninth form, and it is characterized in that, when performing information regeneration and/or recording on the second optical information recording medium, the objective lens When the numerical aperture of the optical system is set as NA2, and the numerical aperture of the objective lens optical system is set as NA3 (NA2>NA3) when performing information reproduction and/or recording on the third optical information recording medium, the The first diffractive structure is formed in a region corresponding to the numerical aperture NA3, and the second diffractive structure is formed in a region corresponding to the numerical aperture NA2 and outside the numerical aperture NA3.

A preferred eleventh form is any one of the objective optical system of the first form to the ninth form, characterized in that, when reproducing and/or recording information on the second optical information recording medium, the When the numerical aperture of the objective optical system is set as NA2, and the numerical aperture of the objective optical system is set as NA3 (NA2>NA3) when performing information regeneration and/or recording on the third optical information recording medium, the The first diffractive structure is formed in a region corresponding to the numerical aperture NA3, and the second diffractive structure is formed in a region corresponding to the numerical aperture NA2.

Two types of formation patterns of the second diffractive structure can be considered. One is the case of forming not in the region corresponding to the numerical aperture NA3 but in the region corresponding to the numerical aperture NA3 to the numerical aperture NA2. In this case, the spherical aberration in the region corresponding to the numerical aperture NA3 needs to be corrected for any one of the first beam, the second beam, and the third beam, but since the wavelength is simultaneously corrected in the first diffraction structure Since the spherical aberration of the three different beams is very difficult, it is preferable to correct the spherical aberration by making the magnification for one of the three beams different from the magnification for the other two beams. Desirable specific ranges of the magnification ratio are the following expressions (4) to (6). Wherein, assume that the magnification of the objective optical system when the first optical information recording medium is used is M1, and the focal length is f1; the magnification of the objective optical system when the second optical information recording medium is used is M2, and the focal length is f2; When the information recording medium is used, the magnification of the objective optical system is M3, and the focal length is f3.

-0.02＜M1×f1＜0.02 (4)

-0.02＜M2×f2＜0.02 (5)

-0.05＜M3×f3＜0.01 (6)

In addition, because the first diffractive structure and the second diffractive structure can be formed on the same optical face, compared with the case where the first diffractive structure and the second diffractive structure are formed on another optical face, it is possible to reduce the Diffraction efficiency decreases due to errors.

The second formation pattern of the second diffractive structure is the case where it is formed over the entire surface of a region corresponding to the numerical aperture NA2. The second diffractive structure has wavelength selectivity to diffract only the second light beam, so it can control only the condensing characteristic of the second light beam without exerting influence on the first light beam or the third light beam. Therefore, when designing the first diffractive structure, only the aberration of the first beam and the third beam can be considered, and the annulus spacing of the first diffractive structure can be determined to optimize the characteristics of the first beam and the third beam . Thereafter, by determining the annular zone pitch of the second diffractive structure so as to optimize the characteristics for the second light beam, it is possible to provide an objective optical system having good characteristics for any light beam.

A preferred twelfth aspect is the objective optical system of the fourth aspect, wherein the numerical aperture of the objective optical system is set to 0 when the information is reproduced and/or recorded on the second optical information recording medium. When NA2, the second diffraction structure is formed on the entire surface corresponding to the area within the numerical aperture NA2, and the diffraction power of the second diffraction structure is positive.

The twelfth aspect involves aperture limitation for the second light beam. On the effect of the eighth form, the same as described about the third light beam, if the diffraction power of the first diffraction structure is negative and its absolute value is large, then the light passing through the area corresponding to the inside of the numerical aperture NA2 The converging position L4 of the second light beam, as shown in the longitudinal spherical aberration diagram of FIG. Between the condensing positions L6 of the second light beam at the outermost periphery E5 of the area corresponding to the outside of the numerical aperture NA2. In this state, on the information recording surface of the second optical information recording medium, on the converging point of the second light beam passing through the area corresponding to the inside of the numerical aperture NA2, the area passing through the outside corresponding to the numerical aperture NA2 is covered. The speckle component may affect the recording and reproduction characteristics.

Here, in order to make the objective optical system have an aperture limiting function for the second light beam, as in the ninth form, in the area corresponding to the outside of the numerical aperture NA2, a wavelength-selective diffraction structure that only diffracts the second light beam can be formed. Consider a design that separates the converging point and the spot component of the second light beam passing through the area corresponding to the inside of the numerical aperture NA2. However, since the wavelength-selective diffraction structure that diffracts only the second light beam has a large number of predetermined step planes formed in the pattern, it is easily affected by a decrease in efficiency or a decrease in transmittance due to a shape error of the diffraction structure. , it is preferable to reduce the area where such diffractive structures are formed. Therefore, as shown in the longitudinal spherical aberration diagram of Fig. 6, it is preferable to make the diffraction power of the second diffractive structure positive, to make the light-condensing position L4 directed to the light-condensing ratio of the spot component passing through the area corresponding to the outside of the numerical aperture NA2 The position closer to the position of the objective optical system is shifted, separating the spot and spot components of the second light beam.

A preferred thirteenth form is the objective optical system described in any one of the first form to the twelfth form, and it is characterized in that the objective optical system further has functions for the first light beam, the second light beam and all The third light beam has a phase structure to which the same amount of optical path difference is added.

In an objective optical system for a high-density optical information recording medium, the amount of aberration generated due to perturbation such as temperature change or incident wavelength change becomes large. For example, spherical aberration due to a change in the refractive index of a material accompanying a temperature change, spherical aberration due to a change in incident wavelength, defocus due to an instantaneous change in incident wavelength, and the like. Therefore, if a phase structure having a function of suppressing such aberrations from occurring in the objective optical system is further designed, the recording and reproducing characteristics during use of a high-density optical information recording medium can be improved. In this case, it is preferable to use a phase structure in which substantially the same amount of optical path difference is added to any of the first light beam, the second light beam, and the third light beam, whereby even when the phase structure is formed, The condensing characteristics of the light beams with respect to the first diffractive structure and the second diffractive structure in the reference state can not be changed. In addition, the "reference state" mentioned here refers to the state where the above-mentioned perturbation does not occur, specifically, the temperature is the design temperature, and, for the objective optical system, refers to the state where the light beam of the design wavelength is incident.

A preferred fourteenth form is the objective optical system of the thirteenth form, characterized in that the same amount of optical path difference is 9.5 to 10.5 times the first wavelength λ1 for the first light beam, preferably 10 times, the second light beam is 5.7 to 6.3 times the second wavelength λ2, preferably 6 times, and the third light beam is 4.8 to 5.2 times the third wavelength λ3, preferably 5 times .

The optical path difference added by the phase structure for each wavelength is preferably 10 times or about 10 times of the first wavelength λ1 for the first light beam, 6 times or about 6 times of the second wavelength λ2 for the second light beam, and 6 times or about 6 times of the second wavelength λ2 for the third beam. The light beam is 5 times or about 5 times the third wavelength λ3. For example, when the first wavelength λ1 is 405nm, the second wavelength λ2 is 655nm, and the third wavelength λ3 is 785nm, if the additional optical path difference is calculated for each light beam, then for the first light beam, it is 405×10=4050nm, For the second light beam at 655×6=3930 nm and for the third light beam at 785×6=3925 nm, the optical path difference is almost the same among the respective wavelengths.

The preferred fifteenth form is the objective optical system of the thirteenth form or the fourteenth form, which is characterized in that the first diffraction structure and the phase structure are formed on the same optical surface, and one of the phase structures Within the annular zone, a predetermined number of annular zones of the first diffraction structure are formed.

By designing such that a predetermined number of annular zones of the first diffractive structure are formed within one annular zone of the phase structure, both structures can be formed on the same optical surface without impairing the functions of the first diffractive structure and the phase structure. Thereby, since the number of optical surfaces on which the diffraction structure and the phase structure are formed is reduced, it is possible to be less affected by a decrease in diffraction efficiency or a decrease in transmittance due to a shape error.

The preferred sixteenth form is the objective optical system of the fifteenth form, which is characterized in that, when m is used as an integer, the optical path difference d _a added to the first light beam by the first diffraction structure, at the The diffraction order p at which the diffraction efficiency of the first light beam in the first diffraction structure becomes maximum, the optical path difference d _l added to the first light beam by the phase structure, and the phase difference for the first light beam in the phase structure The diffraction order s at which the diffraction efficiency of the first light beam becomes the maximum satisfies the following expression (7).

|(d _a /p)/(d _l /s)|＝m (7)

By designing the first diffraction structure and the phase structure so that the value of the formula (7) is an integer, a predetermined number of ring zones of the first diffraction structure can be formed within one ring zone of the phase structure.

A preferred seventeenth aspect is any one of the objective optical systems of the thirteenth aspect to the sixteenth aspect, wherein the cross-sectional shape of the phase structure including the optical axis is stepped. If the phase structure is made into a stepped cross-sectional shape including the optical axis, mold processing is easy, and the shape accuracy of the phase structure can be improved.

A preferred eighteenth aspect is characterized in that any one of the objective optical systems of the first aspect to the seventeenth aspect is mounted on the optical pickup device. According to the eighteenth aspect, an optical pickup device having the same effect as any one of the first to seventeenth aspects can be obtained.

A preferred nineteenth aspect is characterized in that any one of the objective optical systems of the first aspect to the seventeenth aspect is mounted on the optical information recording and reproducing apparatus. According to the nineteenth aspect, an optical information recording and reproducing device having the same effect as any one of the first to seventeenth aspects can be obtained.

A preferred twentieth aspect is described below. An objective optical system used in an optical pickup device, the optical pickup device uses a first light beam of a first wavelength λ1 emitted from a first light source to perform information processing on a first optical information recording medium having a protective layer with a thickness t1 For reproduction and/or recording, for the second optical information recording medium having a protective layer with thickness t2 (t1≤t2), use the second wavelength λ2 (1.5×λ1<λ2<1.7×λ1) emitted from the second light source The second light beam carries out the regeneration and/or recording of information, for the third optical information recording medium with the protective layer of thickness t3 (t2<t3), use the third wavelength λ3 (1.9×λ1<λ3< 2.1 * λ1) the third light beam carries out the regeneration and/or recording of information, it is characterized in that, described objective lens optical system has first diffraction structure and second diffraction structure, and described first diffraction structure makes the p times of first light beam (p is an integer other than 0) the diffracted luminous flux is greater than any other diffracted luminous flux, so that the p-time diffracted luminous flux of the second beam is greater than any other diffracted luminous flux, and the p-time diffracted luminous flux of the third beam is greater than any other order of diffracted luminous flux, at the same time, the second diffraction structure makes the luminous flux of the 0-order diffracted light of the first light beam greater than the luminous flux of any other order of diffracted light, so that the q times of the second light beam (q is the same or different from p Integers other than 0) the luminous flux of the diffracted light is greater than the luminous flux of any other order of diffracted light, so that the luminous flux of the 0-order diffracted light of the third light beam is greater than the luminous flux of any other order of diffracted light. In addition, p is preferably 1. In addition, q is preferably 1.

The first diffractive structure and the second diffractive structure preferably have a stepped cross-sectional shape including the optical axis, but may also be a flared structure (zigzag structure). In addition, the first diffractive structure may also be configured by arranging concentric circles with step-shaped cross-sectional shapes including the optical axis, and moving the steps only by the steps corresponding to the number of steps for each predetermined number of steps. number of heights.

In addition, the first diffractive structure and the second diffractive structure may be arranged on different optical surfaces of the objective optical system, or may be arranged on the same optical surface. The first diffractive structure and the second diffractive structure may overlap on the same optical surface, or be arranged on the same optical surface but not overlap.

In addition, the first diffractive structure and the second diffractive structure may also be arranged on different optical surfaces facing the same optical element included in the objective optical system. Furthermore, when viewing the objective optical system from the direction of the optical axis, at least a part (or all) of the region where the first diffractive structure is provided and the region where the second diffractive structure is provided may also overlap. When viewing the objective optical system from the direction of the optical axis, the area where the first diffractive structure is provided and the area where the second diffractive structure is provided may not overlap at all.

In addition, the objective optical system may also have a plurality of optical elements. At least one of the plurality of optical elements may also be a flat optical element comprising the first diffractive structure and/or the second diffractive structure. At least one of the plurality of optical elements may be a convex lens or a concave lens, but is preferably a convex lens. In addition, it is preferable that the flat optical element has a first diffractive structure and a second diffractive structure. Furthermore, it is preferable that the flat optical element has a third diffractive structure and/or a phase structure.

A preferred twenty-first embodiment will be described below. In the first form or the twentieth form, let NA2 be the numerical aperture of the objective lens optical system on the image side required when carrying out the recording and reproduction of the second optical information recording medium with the second light beam, and NA3 be the numerical aperture of the objective lens optical system on the image side with the third light beam for recording and reproducing the second optical information recording medium. The numerical aperture of the objective lens optical system of the required image side when recording and reproducing the three-optical information recording medium is characterized in that NA2 is greater than NA3, and the first diffraction structure is formed in the area equivalent to NA3, and the second diffraction structure is formed In the area equivalent to NA2. The second diffractive structure may also be formed in a region within NA2 and within NA3. In this case, by forming the first diffractive structure in a region corresponding to NA3, the region where the first diffractive structure is provided and the region where the second diffractive structure is provided overlap when the objective optical system is viewed from the optical axis direction. In addition, the second diffractive structure may also be formed in a region that is inside NA2 but outside NA3. In this case, by forming the first diffractive structure in a region corresponding to NA3, the region where the first diffractive structure is provided and the region where the second diffractive structure is provided do not overlap when the objective optical system is viewed in the optical axis direction. In addition, the second diffractive structure may be formed over the entire surface of the region corresponding to NA2. When the second diffractive structure is formed over the entire surface of the region corresponding to NA2, it is preferable that the diffractive power of the second diffractive structure is positive.

As a preferred twenty-second form, in the first form or the twentieth form, the second diffractive structure is configured such that the cross-sectional shapes including the optical axis are arranged in a concentric circle in a stepped figure, and for each specified Move the steps only by the height of the number of steps corresponding to the number of faces of the class, satisfying the following formula (8).

y×0.95×λ1≤d _b ≤y×1.05×λ1 (8)

In the formula (8), y represents an arbitrary even number, and d _b represents an optical path difference added to the first light beam due to a step difference between adjacent step planes in a stepped pattern. The preferred number of facets is any one of 4, 5, or 6. In addition, y is preferably 2. It is more preferable to satisfy the following formula (8)'.

d _b =y×λ1 (8)'

As a preferred twenty-third aspect, in the first aspect or the twentieth aspect, the objective optical system has a third diffractive structure. In addition, the third diffraction structure is characterized in that the luminous flux of the 0-order diffracted light of the first beam is greater than the luminous flux of any other order of diffracted light, and the luminous flux of the 0-order diffracted light of the second beam is greater than that of any other order of diffracted light The luminous flux is such that the luminous flux of the r-time (r is an integer other than 0 that is the same as or different from p) of the third light beam is greater than the luminous flux of any other order of diffracted light. In addition, r is preferably 1.

In addition, the first diffractive structure and the third diffractive structure may be provided on the same optical plane of the objective optical system. In this case, the first diffractive structure and the third diffractive structure may be provided so as to overlap each other on the same optical surface. On the other hand, the second diffractive structure and the third diffractive structure may also be provided in the same optical plane. In this case, the second diffractive structure and the third diffractive structure may be provided so as to overlap each other on the same optical surface. In addition, the third diffractive structure may also be arranged in an optical plane different from that of the first diffractive structure and the second diffractive structure.

A preferred twenty-fourth aspect is described below. In the twenty-third form, NA1 is set to be the numerical aperture of the objective optical system on the image side required when recording and reproducing the first optical information recording medium using the first light beam, and NA3 is set to use the third light beam to perform the first optical information recording medium. When the numerical aperture of the objective optical system on the image side required for recording and reproducing the three-optical information recording medium, NA1 is larger than NA3, the first diffractive structure is formed in a region corresponding to NA3, and the third diffractive structure is formed in a region corresponding to NA3. outside the area.

A preferred twenty-fifth embodiment is described below. In the twenty-third aspect, the third diffractive structure is a binary structure of binary values, and the optical path difference _dc added to the first light beam by one step difference of the binary structure satisfies the following formula (9).

4.8×λ1≤d _c ≤5.2×λ1 (9)

A preferred twenty-sixth aspect is described below. In the first aspect or the twentieth aspect, the objective optical system has a phase structure and satisfies the following expressions (10), (11), (12), (13), and (14).

a×0.95×λ1≤d ₁ ≤a×1.05×λ1 (10)

b×0.95×λ2≤d ₂ ≤b×1.05×λ2 (11)

c×0.95×λ3≤d ₃ ≤c×1.05×λ3 (12)

0.9×d ₁ ≤d ₂ ≤1.1×d ₁ (13)

0.9×d ₁ ≤d ₃ ≤1.1×d ₁ (14)

a represents an arbitrary positive integer, b represents an arbitrary positive integer smaller than a, and c represents an arbitrary positive integer smaller than b. d ₁ represents the optical path difference of the first beam produced by one step difference of the phase structure, d ₂ represents the optical path difference of the second beam produced by one step difference of the phase structure, d ₃ represents one step difference of the phase structure The resulting optical path difference of the third beam. In addition, when λ1 is greater than or equal to 350 nm and less than or equal to 440 nm, λ2 is greater than or equal to 570 nm and less than or equal to 670 nm, and λ3 is greater than or equal to 750 nm and less than or equal to 880 nm, (more preferably when λ1 is greater than or equal to 390 nm and less than or equal to 415 nm, When λ2 is 630 nm or more and 670 nm or less, and λ3 is 750 nm or more and 820 nm or less), a is preferably 10, b is 6, and c is 5. In addition, it is preferable that the depth of one step of the phase structure in the direction of the optical axis is equal to or greater than 3800 nm and equal to or less than 4200 nm. In addition, it is preferable that the depth of one step of the phase structure in the direction of the optical axis is an integer multiple or substantially an integer multiple of the least common multiple of λ1, λ2, and λ3.

In addition, among the formulas (13) and (14), it is more preferable to satisfy the following formulas (13)' and (14)'.

0.95×d ₁ ≤d ₂ ≤1.05×d ₁ (13)'

0.95×d ₁ ≤d ₃ ≤1.05×d ₁ (14)'

In addition, the phase structure preferably has a stepped cross section including the optical axis, and may also be a flare structure (zigzag structure). In addition, the first diffractive structure and the phase structure may overlap on the same optical plane, or the second diffractive structure and the phase structure may overlap on the same optical plane. In addition, the third diffraction structure and the phase structure may overlap on the same optical plane.

In addition, when the diffracted luminous flux of the s times (s is an integer other than 0) of the first beam is greater than the diffracted luminous flux of any other times, and the t times (t is an integer other than 0, different from s) of the second beam of diffraction When the luminous flux is greater than the diffracted luminous flux of any other order, so that the u-order (u is an integer other than 0, different from s and t) of the third light beam is greater than the diffracted luminous flux of any other order, the preferred phase structure satisfies the following formula (15).

|(d _a /p)/(d _l /s)|＝m (15)

m represents a positive integer, d _a represents the optical path difference added to the first light beam by the first diffraction structure, and d _l represents the optical path difference added to the first light beam by the phase structure.

A preferred twenty-seventh embodiment is described below. In the twenty-sixth aspect, the first diffractive structure and the phase structure are provided on the same optical plane of the objective optical system, and a predetermined number of annular zones of the first diffractive structure are formed in one annular zone of the phase structure. That is, in this form, both the phase structure and the first diffractive structure have multiple rings, but one ring of the phase structure, which is larger than the one ring of the first diffractive structure, contains in one ring of the phase structure A plurality of annular bands of the first diffractive structure.

A preferred twenty-eighth embodiment will be described below. The objective optical system is characterized in that it includes superimposing the cross-sectional shapes including the optical axis in a stepped shape arranged in concentric circles, and making the cross-sectional shapes including the optical axis in one step of the stepped figures. A structure in which small stepped figures are arranged in concentric circles. Furthermore, as shown in FIG. 13 , a large stepped figure that can also be composed of a plurality of larger steps is that as the optical axis approaches the optical axis in the direction perpendicular to the optical axis, in the direction of the optical axis A structure extending downward in a direction towards the interior of the objective optical system. A small stepped figure composed of multiple smaller steps (a smaller step) is, within the scope of a larger step, as it approaches the optical axis in the direction perpendicular to the optical axis, in the direction of the optical axis A structure extending upward in a direction towards the outside of the objective optical system. A large ladder-like figure or a small ladder-like figure is also good, and the number of steps is arbitrary. In addition, it is good to have a large ladder-shaped graph or a small ladder-shaped graph, and it may be periodic or non-periodic.

Furthermore, as shown in FIG. (13), when a large staircase pattern and a small staircase pattern overlap, it is preferable to satisfy the following expressions (16) and (17).

0.9<dp×(n-1)/λ1<1.5 (16)

9.8<DP×(n-1)/λ1<10.2 (17)

dp represents the depth in the direction of the optical axis of the level difference of the small stair-shaped pattern shown in FIG. 13 . DP represents the depth in the direction of the optical axis of the level difference of the large stepped pattern shown in FIG. 13 . n represents the refractive index under the first light beam of the optical material of the objective optical system provided with the stepped pattern.

Furthermore, it is preferable that the second diffraction structure satisfies the following formula (18).

1.9<dp ₂ ×(n _x -1)/λ1<2.1 (18)

dp ₂ represents the depth in the optical axis direction of one step difference of the second diffractive structure. n _x represents the refractive index under the first light beam of the optical material on which the second diffractive structure is provided.

A preferred twenty-ninth form is an optical pickup device, characterized in that it has: a device for emitting a first light beam of a wavelength λ1 for recording and/or reproducing a first optical information recording medium having a protective layer having a thickness t1. The first light source emits a second light source of a wavelength λ2 (1.5×λ1<λ2<1.7×λ1) for recording and/or reproducing a second optical information recording medium having a protective layer having a thickness of t2 (t1≤t2). The second light source of the light beam emits the wavelength λ3 (1.9×λ1<λ3<2.1×λ1) for recording and/or reproducing the third optical information recording medium having a protective layer with a thickness of t3 (t2<t3). The third light source of the third light beam is further equipped with any objective optical system of the twentieth form to the twenty-eighth form.

A preferred thirtieth aspect is an optical information recording and reproducing apparatus, which is characterized in that the optical pickup device of the twenty-ninth aspect is incorporated.

According to the present invention, it is possible to provide an objective lens capable of satisfactorily correcting spherical aberration required for compatibility between high-density optical disks, DVDs, and CDs without sacrificing various characteristics such as the wavelength dependence of spherical aberration and track tracking characteristics. An optical system, an optical pickup device using the objective optical system, and an optical information recording and reproducing device equipped with the optical pickup device.

Description of drawings

FIG. 1 is a longitudinal spherical aberration diagram of the third wavelength λ3.

Fig. 2 is a light spot diagram on an information recording surface of a third optical information recording medium.

Fig. 3 is a diagram of longitudinal spherical aberration at the third wavelength λ3.

Fig. 4 is a light spot diagram on an information recording surface of a third optical information recording medium.

Fig. 5 is a diagram of longitudinal spherical aberration at the second wavelength λ2.

FIG. 6 is a diagram of longitudinal spherical aberration at the second wavelength λ2.

Fig. 7 is a plan view of main parts showing the structure of the optical pickup device.

FIG. 8 is a diagram showing the configuration of an objective optical system.

Fig. 9 is a plan view of main parts showing the structure of the optical pickup device.

FIG. 10 is a diagram showing the configuration of an objective optical system.

Fig. 11 is a diagram showing longitudinal spherical aberration of a red laser beam.

Fig. 12 is a diagram showing longitudinal spherical aberration of an infrared laser beam.

FIG. 13 is a diagram showing a part of the configuration of an objective optical system.

Symbol Description

PU, PU2 optical pickup device

OL, OL2 objective lens optical system

CL collimation optical system

BE Extended Optical System

BE1 first lens

SE Sensing Optical System

PD light detector

AC1 double shaft transmission

AC2 single shaft transmission

P1 first prism

P2 second prism

P3 third prism

ML upward mirror

L1 aberration correction element

L2 concentrator

HL barrel (holding part)

STO aperture

DOE1 first diffraction structure

DOE2 Second Diffraction Structure

DOE3 third diffraction structure

DOE4 phase structure

LD1 blue-violet semiconductor laser (first light source)

LD2 red semiconductor laser (second light source)

LD3 infrared semiconductor laser (third light source)

BD's first optical information recording medium (high-density optical information recording medium. High-density optical disc)

DVD Second Optical Information Recording Medium

CD third optical information recording medium

PL1, PL2, PL3 protection layer

RL1, RL2, RL3 information recording surface

Detailed ways

[First Embodiment]

Next, a first embodiment of the present invention will be described using the drawings. First, an optical pickup device using an objective optical system according to an example of the present invention will be described with reference to FIG. 7 .

Fig. 7 is a schematic representation no matter for high-density optical information recording medium BD (the first optical information recording medium) and DVD (the second optical information recording medium) and CD (the third optical information recording medium) any one can carry out appropriate A diagram showing the configuration of an optical pickup device PU for recording and reproducing information. The specification of BD is that the first wavelength λ1=405nm, the thickness t1=0.1mm of the protective layer PL1, and the numerical aperture NA1=0.85; the specification of the DVD is that the second wavelength λ2=655nm, the thickness t2 of the protective layer PL2=0.6mm, Numerical aperture NA2 = 0.65; CD specifications are: third wavelength λ3 = 785 nm, thickness t3 of protective layer PL3 = 1.2 mm, and numerical aperture NA3 = 0.51. However, the combination of the wavelength, the thickness of the protective layer, and the numerical aperture is not limited thereto.

The optical pick-up unit PU comprises: blue-violet semiconductor laser LD1 (first light source) for BD, red semiconductor laser LD2 (second light source) for DVD, infrared semiconductor laser LD3 (third light source) for CD, BD/DVD/ CD-shared photodetector PD, objective optical system OL, collimating optical system CL, dual-axis transmission device AC1, single-axis transmission device AC2, first prism P1, second prism P2, third prism P3, lifting mirror ML, The sensor optical system SE which adds astigmatism to the light beam reflected from the information recording surface of each optical information recording medium. In addition, a blue-violet SHG laser can also be used as a light source for BD.

In the optical pickup device PU, in the case of recording/reproducing information on a BD, the position of the collimating optical system CL is adjusted in the direction of the optical axis by the single-axis actuator AC2 so that the collimating optical system CL receives a parallel light beam. After the blue-violet laser beam is emitted, the blue-violet semiconductor laser LD1 emits light. The divergent light beam emitted from the blue-violet semiconductor laser LD1, as shown in Figure 7 with a solid line to describe its light path, is reflected by the first prism P1, passes through the second prism P2 and the third prism P3 in sequence, and passes through the collimating optical system CL Convert to parallel beams. Thereafter, after being reflected by the lifting mirror ML, the beam diameter is limited by the diaphragm STO, and becomes a light spot formed on the information recording surface RL1 via the protective layer PL1 of the BD by the objective optical system OL. The objective optical system OL performs focusing or track tracking through the biaxial transmission device AC1 arranged around it. In addition, the objective optical system OL will be described in detail later.

The reflected beam modulated by the information pits on the information recording surface RL1 passes through the objective optical system OL again, is reflected by the lifting mirror ML, and becomes a converging beam when passing through the collimating optical system CL. Thereafter, after passing through the third prism P3, the second prism P2, and the first prism P1 in sequence, the astigmatism is added by the sensing optical system SE and converges on the photosensitive surface of the photodetector PD. The information recorded on the BD can be read using the output signal of the photodetector PD.

In addition, in the optical pickup device PU, in the case of recording/reproducing information on a DVD, the position of the collimating optical system CL is adjusted in the direction of the optical axis by the single-axis actuator AC2 so that the collimating optical system CL is After the red laser beam is emitted in the parallel beam state, the red semiconductor laser LD2 is made to emit light. The divergent light beam emitted from the red semiconductor laser LD2 is reflected by the second prism P2, passes through the third prism P3, and is converted into a parallel light beam by the collimating optical system CL as shown in FIG. Then, after being reflected by the lifting mirror ML, it becomes the light spot formed on the information recording surface RL2 via the protective layer PL2 of DVD by the objective optical system OL. The objective optical system OL performs focusing or track tracking through the biaxial transmission device AC1 arranged around it.

The reflected beam modulated by the information pits on the information recording surface RL2 passes through the objective optical system OL again, is reflected by the lifting mirror ML, and becomes a converging beam when passing through the collimating optical system CL. Thereafter, after passing through the third prism P3, the second prism P2, and the first prism P1 in sequence, the astigmatism is added by the sensing optical system SE and converges on the photosensitive surface of the photodetector PD. The information recorded on the DVD can be read using the output signal of the photodetector PD.

In addition, in the optical pickup device PU, in the case of recording/reproducing information on a CD, the position of the collimating optical system CL is adjusted in the direction of the optical axis by the single-axis actuator AC2 so that the collimating optical system CL is After the infrared laser beam is emitted in the state of parallel beams, the infrared semiconductor laser LD3 is made to emit light. The diverging light beam emitted from the infrared semiconductor laser LD3 is reflected by the third prism P3 as its light path is drawn by a dotted line in FIG. Then, after being reflected by the lifting mirror ML, it becomes the light spot formed on the information recording surface RL3 via the protective layer PL3 of CD by the objective optical system OL. The objective optical system OL performs focusing or track tracking through the biaxial transmission device AC1 arranged around it.

The reflected beam modulated by the information pits on the information recording surface RL2 passes through the objective optical system OL again, is reflected by the lifting mirror ML, and becomes a converging beam when passing through the collimating optical system CL. Thereafter, after passing through the third prism P3, the second prism P2, and the first prism P1 in sequence, the astigmatism is added by the sensing optical system SE and converges on the photosensitive surface of the photodetector PD. The information recorded on the CD can be read using the output signal of the photodetector PD.

In the optical pickup device PU, by driving the collimator optical system CL in the optical axis direction by the uniaxial actuator AC2, spherical aberration at the time of BD use can be corrected. With such a spherical aberration correction mechanism, it is possible to correct wavelength dispersion due to manufacturing errors of the blue-violet semiconductor laser LD1, refractive index change or refractive index distribution of the objective optical system accompanied by temperature changes, and gap between information recording layers of a multilayer disc. Spherical aberration caused by focus jump, thickness dispersion due to manufacturing error of the protective layer PL1 or thickness distribution, and the like. In addition, with this spherical aberration correcting mechanism, it is also possible to correct spherical aberration when using a DVD or when using a CD.

Next, the structure of the objective optical system OL will be described. FIG. 8 schematically shows the structure of the objective optical system OL according to the present invention. The objective optical system OL has a structure in which the aberration correcting element L1 and the condensing element L2 arranged sequentially from the laser light source side are held coaxially around the optical axis X by the lens barrel (holding member) HL.

The aberration correcting element L1 is a plastic lens in which a stepped diffraction structure and a phase structure are provided on a flat optical element, and the optical surface of the plastic lens on the optical information recording medium side is divided into a central region C1 corresponding to the numerical aperture NA3. , and equivalent to or greater than the numerical aperture NA3, the surrounding area C2 in the numerical aperture NA1, the optical surface of the laser light source side of the plastic lens is divided into a central area C3 corresponding to the numerical aperture NA2, and a value equal to or greater than the numerical aperture NA2, the surrounding area C4 within the numerical aperture NA1.

In the central area C1 of the optical surface on the optical information recording medium side, the first diffractive structure DOE1 for correcting the spherical aberration caused by the different thicknesses of the protective layer PL1 and the protective layer PL3 is formed, and on a part of the surrounding area C2, A third diffraction structure DOE3 is formed on the information recording surface RL3 for separating the converging point of the third light beam by the first diffraction structure DOE1 and the spot component of the third light beam passing through the area outside the numerical aperture NA3. In addition, a phase structure DOE4 is formed on the entire optical surface on the side of the optical information recording medium to suppress defocus errors that occur when the wavelength of the blue-violet laser light source changes instantaneously when used in BD. Therefore, in this embodiment, the phase structure overlaps with the first diffraction structure, and also the phase structure overlaps with the third diffraction structure.

In addition, on the central region C3 of the optical surface on the side of the laser light source, a second diffractive structure DOE2 for correcting the spherical aberration caused by the different thicknesses of the protective layer PL1 and the protective layer PL2 is formed, and the surrounding region C4 becomes a place where no diffractive structure is formed. Or the plane of the fine structure such as the phase structure. Therefore, in the present embodiment, when the objective optical system is viewed from the optical axis direction, the first diffractive structure and the second diffractive structure overlap each other.

The cross-sectional shape including the optical axis of the first diffractive structure DOE1 is made into a stepped shape, and the depth d of the step along the optical axis is taken as 1.096 μm. In addition, the flare wavelength λB of the first diffractive structure DOE1 is 550 nm. In the first diffraction structure DOE1, the diffraction order at which the diffraction efficiency becomes the maximum is 1 for any beam, and the diffraction efficiency of the first-order diffracted light for each beam is 58.2% for the blue-violet laser beam and 91.0% for the red laser beam. , 72.0% for infrared laser beams. The ring pitch of the first diffractive structure DOE1 is optimized to well correct the spherical aberration caused by the difference in thickness of the protective layer PL1 and the protective layer PL3 .

In addition, the second diffractive structure DOE2 is a structure in which the cross-sectional shape including the optical axis is arranged in a stepped shape concentrically, and the steps are moved by only 4 steps for every 5 steps. The difference was set to be twice the first wavelength λ1 in terms of optical path difference, and the depth d in the optical axis direction was set to 1.571 μm. The second diffraction structure DOE2 is a wavelength-selective diffraction structure that diffracts only the second beam as first-order diffracted light. The transmittance (diffraction efficiency of 0-order diffracted light) of the blue-violet laser beam is 100%. The diffraction efficiency of the first-order diffracted light of the beam was 87.2%, and the transmittance of the infrared laser beam was 99.0%. The annular zone pitch of the second diffractive structure DOE2 is optimized to well correct the spherical aberration caused by the difference in thickness of the protective layer PL1 and the protective layer PL2 . In addition, the diffraction capability of the second diffractive structure DOE2 is set to be positive, and its absolute value is determined as follows: on the information recording surface RL2, in order to make the red laser beam passing through the first diffractive structure DOE1 and the second diffractive structure DOE2 focus on the The spot component passing through the area outside the numerical aperture NA2 has a sufficiently separated spot component (refer to FIG. 6 ), so that the red laser beam incident on the objective optical system OL can automatically perform aperture limitation corresponding to the numerical aperture NA2.

Here, the principle of diffraction based on the second diffraction structure DOE2 will be described. Because the depth d in the optical axis direction of a step difference in the graph is 1.571 μm, the additional optical path difference for the blue-violet laser beam through the step difference becomes twice the first wavelength λ1, and the additional light for the infrared laser beam The path difference becomes 1 time of the third wavelength λ3, and both the blue-violet laser beam and the infrared laser beam are transmitted without diffraction. On the other hand, the optical path difference added to the red laser beam by this step difference becomes about 1.2 times the second wavelength λ2. Since the substantial optical path difference after subtracting the optical path difference of 1 wavelength at equal phase is about 0.2 times the second wavelength λ2, the wavefront of the red laser beam passing through the adjacent step plane deviates by about 0.2 wavelength. The optical path difference in the pattern composed of five stages as a whole is about 1 time (0.2×5) of the second wavelength λ2, so the wavefronts passing through adjacent patterns deviate by 1 wavelength and overlap, and become in the primary direction Diffraction of diffracted light.

The third diffractive structure DOE3 is a binary structure, and the depth d in the direction of the optical axis taking one step difference is 3.928 μm. This depth is equivalent to 5 times the first wavelength λ1 in terms of optical path difference, and is also equivalent to 3 times the second wavelength λ2. Therefore, both the blue-violet laser beam and the red laser beam are transmitted without diffraction. On the other hand, the optical path difference added to the infrared laser beam due to the step difference becomes about 2.5 times the third wavelength λ3, so the incident third beam is diffracted as ±1st order diffracted light. The ring zone pitch of the third diffractive structure is determined to: on the information recording surface RL3, the spot component of the infrared laser beam based on the first diffractive structure DOE1 and the spot component of the third beam passing through the surrounding area C2 and the surrounding area C4 are well separated (Refer to FIG. 3 and FIG. 4 ), therefore, the aperture limitation corresponding to the numerical aperture NA3 is automatically performed on the infrared laser beam incident on the objective optical system OL.

The cross-sectional shape including the optical axis of the phase structure DOE4 is made into a stepped shape, and the depth d of the step along the optical axis is taken to be 7.857 μm. In addition, the flare wavelength λB of the phase structure DOE4 is 405nm. The phase structure DOE4 is configured such that the diffraction order at which the diffraction efficiency becomes maximum is 10 for the violet laser beam, 6 for the red laser beam, and 5 for the infrared laser beam. This phase structure DOE4 adds substantially the same amount of phase difference to any beam, so the diffraction efficiency is almost 100% for any beam. The phase structure DOE4 is a structure for suppressing the chromatic aberration of the objective optical system OL, and even when the mode hopping is caused by the blue-violet laser light source LD1, since the defocus error on the information recording surface RL1 can be suppressed to be small, it can be used for BD obtains stable recording and reproduction characteristics.

In addition, the area ratio of the central region C1 to the entire optical surface on the laser side is {(0.51/0.85) ² }×100=36%. Therefore, if the diffraction efficiency of the blue-violet laser beam on the optical surface on the laser side is calculated, it becomes {0.582*0.36+1*(1-0.36)}*100=85.0%. Like this, even under the situation of paying attention to the diffraction efficiency of the first diffraction structure DOE1 for infrared laser beam, because the area ratio of the central region C1 of the effective diameter for blue-violet laser beam is very small, so can guarantee the effective of blue-violet laser beam high enough. Efficiency average within diameter.

[Second Embodiment]

Next, a second embodiment of the present invention will be described using the drawings. First, an optical pickup device using an objective optical system according to another example of the present invention will be described with reference to FIG. 9 .

The optical pick-up device PU2 that schematically shows among Fig. 9 has following several characteristics: For the point that the infrared laser beam of objective lens optical system OL2 is incident with the state of divergent beam, it is used as spherical aberration correcting mechanism with the ability to pass through uniaxial actuator AC2 on the light beam. The expansion optical system of the structure that drives the first lens BE1 on the laser light source side in the axial direction, and the point that the weakly divergent light beam enters the objective optical system OL2 when recording/reproducing information on a CD.

The optical pick-up unit PU2 comprises: blue-violet semiconductor laser LD1 (first light source) for BD, red semiconductor laser LD2 (second light source) for DVD, infrared semiconductor laser LD3 (the third light source) for CD, BD/DVD/ CD-shared photodetector PD, objective optical system OL2, collimating optical system CL, extended optical system BE, dual-axis transmission device AC1, single-axis transmission device AC2, first prism P1, second prism P2, third prism P3, Lifting mirror ML and sensing optical system SE for adding astigmatism to light beams reflected from the information recording surface of each optical information recording medium. In addition, a blue-violet SHG laser can also be used as a light source for BD.

In the optical pickup device PU2, in the case of recording/reproducing information on a BD, the position of the first lens BE1 is adjusted in the direction of the optical axis by the single-axis actuator AC2 so that the beam from the extended optical system BE is parallel to the state of the light beam. After the blue-violet laser beam is emitted, the blue-violet semiconductor laser LD1 is made to emit light. The divergent light beam emitted from the blue-violet semiconductor laser LD1, as shown in Fig. 9 with a solid line to describe its ray path, is reflected by the first prism P1, and then passes through the second prism P2 and the third prism P3 in sequence, and is transmitted by the collimating optical system CL transforms into a parallel beam. Thereafter, due to the extended optical system BE, it becomes a parallel beam with an enlarged diameter, and after being reflected by the lifting mirror ML, the diameter of the beam is limited by the diaphragm STO, and passes through the objective optical system OL2 to become the light formed on the information recording surface RL1 via the protective layer PL1 of the BD. point. The objective optical system OL2 performs focusing or track tracking through the biaxial transmission device AC1 arranged around it. In addition, the objective optical system OL2 will be described in detail later.

The reflected light beam modulated by the information pit on the information recording surface RL1 passes through the objective optical system OL2 again, is reflected by the lifting mirror ML, is reduced in diameter by the expanding optical system BE, and becomes a converging light beam when passing through the collimating optical system CL. Thereafter, after passing through the third prism P3 , the second prism P2 and the first prism P1 sequentially, the astigmatism is added by the sensing optical system SE and converges on the photosensitive surface of the photodetector PD. The information recorded on the BD can be read using the output signal of the photodetector PD.

In addition, in the optical pickup device PU2, in the case of recording/reproducing information on a DVD, the position of the first lens BE1 is adjusted in the direction of the optical axis by the uniaxial actuator AC2 so that the parallel light beam from the expansion optical system BE After the red laser beam is emitted, the red semiconductor laser LD2 is made to emit light. The divergent light beam emitted from the red semiconductor laser LD2 is reflected by the second prism P2 as shown by the broken line in FIG. Thereafter, it is converted into a parallel light beam while expanding its diameter by the expanding optical system BE, reflected by the lifting mirror ML, and becomes a light spot formed on the information recording surface RL2 through the protective layer PL2 of DVD by the objective optical system OL2. The objective optical system OL2 performs focusing or track tracking through the biaxial transmission device AC1 arranged around it.

The reflected light beam modulated by the information pit on the information recording surface RL2 passes through the objective optical system OL2 again, is reflected by the lifting mirror ML, is reduced in diameter by the expanding optical system BE, and becomes a converging light beam when passing through the collimating optical system CL. Thereafter, after passing through the third prism P3 , the second prism P2 and the first prism P1 sequentially, the astigmatism is added by the sensing optical system SE and converges on the photosensitive surface of the photodetector PD. The information recorded on the DVD can be read using the output signal of the photodetector PD.

In addition, in the optical pickup device PU2, in the case of recording/reproducing information on a CD, the position of the first lens BE1 is adjusted in the direction of the optical axis by the uniaxial actuator AC2 so that it can be slightly divergent from the expansion optical system BE. Beam state After the infrared laser beam is emitted, the infrared semiconductor laser LD3 is made to emit light. The diverging light beam emitted from the infrared semiconductor laser LD3 is reflected by the third prism P3 as shown in FIG. 9 with a dashed line, and then transformed into a substantially parallel light beam by the collimating optical system CL. Thereafter, it is converted into a weakly divergent light beam while being enlarged in diameter by the expanding optical system BE, reflected by the lifting mirror ML, and becomes a light spot formed on the information recording surface RL3 via the protective layer PL3 of the CD through the objective optical system OL2. The objective optical system OL2 performs focusing or track tracking through the biaxial transmission device AC1 arranged around it.

The reflected light beam modulated by the information pit on the information recording surface RL2 passes through the objective optical system OL2 again, is reflected by the lifting mirror ML, is reduced in diameter by the expanding optical system BE, and becomes a converging light beam when passing through the collimating optical system CL. Thereafter, after passing through the third prism P3 , the second prism P2 and the first prism P1 sequentially, the astigmatism is added by the sensing optical system SE and converges on the photosensitive surface of the photodetector PD. The information recorded on the CD can be read using the output signal of the photodetector PD.

In the optical pickup device PU2, by driving the first lens BE1 of the expansion optical system BE in the optical axis direction by the uniaxial actuator AC2, spherical aberration at the time of BD use can be corrected. With such a spherical aberration correction mechanism, it is possible to correct wavelength dispersion due to manufacturing errors of the blue-violet semiconductor laser LD1, refractive index change or refractive index distribution of the objective optical system accompanied by temperature changes, and gap between information recording layers of a multilayer disc. Spherical aberration caused by focus jump, thickness dispersion due to manufacturing error of the protective layer PL1 or thickness distribution, and the like. In addition, with this spherical aberration correcting mechanism, it is also possible to correct spherical aberration when using a DVD or when using a CD.

Next, the structure of the objective optical system OL2 will be described. The objective optical system OL2 that Fig. 10 schematically shows has such feature, promptly on the optical surface of optical information recording medium side, only forms the second diffractive structure DOE2 in the area corresponding to greater than or equal to numerical aperture NA3, numerical aperture NA2.

The optical surface of the laser light source side of the aberration correcting element L1 which is a flat optical element is divided into a central region C5 corresponding to the numerical aperture NA3, and a peripheral region C6 corresponding to the numerical aperture NA1 equal to or greater than the numerical aperture NA3. , the optical surface on the side of the optical information recording medium is divided into a central area C7 corresponding to the numerical aperture NA3, a surrounding area C8 corresponding to the numerical aperture NA3 or greater, and a surrounding area C8 in the numerical aperture NA2, and a numerical aperture NA2 or greater. The surrounding area C9 within the numerical aperture NA1.

In the central region C5 of the optical surface on the side of the laser light source, a first diffraction structure DOE1 for correcting the spherical aberration caused by the different thicknesses of the protective layer PL1 and the protective layer PL2 and the protective layer PL3 is formed. On the entire surface, a phase structure DOE4 is formed to suppress the defocus error that occurs when the wavelength of the blue-violet laser light source changes momentarily when the BD is used. In addition, on the peripheral area C8 of the optical surface of the optical information recording medium, a second diffractive structure DOE2 for correcting spherical aberration caused by the thickness difference between the protective layer PL1 and the protective layer PL2 is formed.

The ring pitch of the first diffractive structure DOE1 is optimized to well correct the spherical aberration caused by the different thicknesses of the protective layer PL1 and the protective layer PL2 . In this way, the first diffractive structure DOE1 is optimized to well correct the spherical aberration caused by the different thicknesses of the protective layer PL1 and the protective layer PL2. The correction of the spherical aberration becomes insufficient, and the spherical aberration caused by the difference in thickness between the protective layer PL1 and the protective layer PL3 remains on the information recording surface RL3. Therefore, when recording and reproducing information on a CD, the spherical aberration caused by the thickness difference between the protective layer PL1 and the protective layer PL3 is completely corrected by entering the infrared laser beam into the objective optical system OL2 with a weakly divergent beam.

In addition, the ring pitch of the second diffractive structure DOE2 is optimized to correct the spherical aberration caused by the thickness difference between the protective layer PL1 and the protective layer PL2 for the red laser beam passing through the surrounding area C8 of the optical surface on the laser source side.

The phase structure DOE4 is the same in function and structure as the phase structure DOE4 of the objective optical system OL in the first embodiment, so detailed description thereof will be omitted here.

In addition, if the diffraction ability of the first diffractive structure DOE1 is negative but its absolute value is too large, as shown in the longitudinal spherical aberration diagram of Figure 1 or Figure 5, the red laser beam or the infrared laser beam outside the effective diameter If the spot component of the region overlaps with the light-converging point, there is a possibility that good recording and reproduction characteristics cannot be obtained. Therefore, in the present objective optical system OL2, the absolute value of the diffractive power is determined so that the converging point does not overlap with the spot component passing through the region outside the effective diameter (see FIG. 11 and FIG. 12 ). This makes it possible to automatically perform aperture limitation corresponding to the respective numerical apertures of the red laser beam or the infrared laser beam incident on the objective optical system OL2.

In addition, in the above-mentioned first embodiment and second embodiment, the structure in which three laser light sources are independently arranged respectively is adopted, but it is also possible to use a laser light source in which three laser light sources are placed in one frame, or a laser light source on the same chip. A laser light source that forms 3 laser light emitting points. In addition, in the optical pickup units PU and PU2, the laser light source and the photodetector are arranged independently, but an element in which the laser light source and the photodetector are integrated may also be used. In addition, in the optical pickup units PU, PU2, a phase control element using a liquid crystal may also be used as a spherical aberration correction mechanism. Since a method of correcting spherical aberration using such a phase control element is known, a detailed description thereof will be omitted here.

In the above embodiment, the objective optical system and the optical pick-up device capable of recording/reproducing the three kinds of optical discs of the high-density optical information recording medium BD, DVD, and CD have been described as examples, but the present invention can also be applied to The objective lens optical system, the optical pickup device, and the optical information recording and reproducing device for recording/reproducing the two types of high-density optical information recording media BD and DVD, or the two types of high-density optical information recording media BD and CD are easy. understand.

For example, the optical system elements required for the recording/reproduction of two kinds of optical discs can be kept and other optical elements are formed, thereby, a small, light in weight, low cost, simple in structure optical pickup optical system and optical pickup device can be realized. .

In addition, HD or other high-density optical disks may be used instead of BD.

In addition, the present invention is not limited to the examples described in the specification, and it is clear for those skilled in the art that other examples and modified examples are included from the examples and concepts described in the specification. The descriptions and examples in the specification are for illustrative purposes only, and the scope of the present invention is indicated by the claims.

Claims (37)

1. the objective lens optical system that uses in the optical take-up apparatus; described optical take-up apparatus is for first optical information recording medium of the protective seam with thickness t 1; the regeneration and/or the record of information carried out in use from first light beam of first wavelength X 1 of first light source ejaculation; second optical information recording medium for protective seam with thickness t 2; the regeneration and/or the record of information carried out in use from second light beam of second wavelength X 2 of secondary light source ejaculation; the 3rd optical information recording medium for protective seam with thickness t 3; the regeneration and/or the record of information carried out in use from the 3rd light beam of the wavelength lambda 3 of the 3rd light source ejaculation; wherein; t1≤t2; 1.5 * λ 1＜λ 2＜1.7 * λ 1; t2＜t3; 1.9 * λ 1＜λ 3＜2.1 * λ 1 is characterized in that

Described objective lens optical system has first diffraction structure and second diffraction structure,

Described first diffraction structure makes the diffraction light flux of other any number of times of diffraction light flux ratio of p time of described first light beam all big, make the diffraction light flux of other any number of times of diffraction light flux ratio of p time of described second light beam all big, make the diffraction light flux of other any number of times of diffraction light flux ratio of p time of described the 3rd light beam all big, wherein p is the integer beyond 0

Described second diffraction structure makes the luminous flux of diffraction light of other any number of times of light flux ratio of 0 time diffraction light of described first light beam all big, make the luminous flux of diffraction light of other any number of times of light flux ratio of q time diffraction light of described second light beam all big, make the luminous flux of diffraction light of other any number of times of light flux ratio of 0 time diffraction light of described the 3rd light beam all big, wherein q is the integer beyond identical or different with p 0.

2. objective lens optical system according to claim 1 is characterized in that described p is 1.

3. objective lens optical system according to claim 1 is characterized in that described q is 1.

4. objective lens optical system according to claim 2 is characterized in that, the credit light wavelength lambda B of described first diffraction structure satisfies following formula:

λ1＜λB＜λ3。

5. objective lens optical system according to claim 4, it is characterized in that, the numerical aperture of the information of the regeneration carry out to(for) described first optical information recording medium and/or the described objective lens optical system in when record is made as NA1, the information of regeneration carry out to(for) described the 3rd optical information recording medium and/or the numerical aperture of the described objective lens optical system when writing down when being made as NA3, satisfy the following conditions formula:

1.25×λ1＜λB＜0.95×λ2

NA1＞NA3

NA3/NA1＜0.7。

6. objective lens optical system according to claim 1 is characterized in that, the diffracting power of described first diffraction structure is for negative.

7. objective lens optical system according to claim 1 is characterized in that, the cross sectional shape that described first diffraction structure comprises optical axis is stepped.

8. objective lens optical system according to claim 1, it is characterized in that, described second diffraction structure be the cross sectional shape that comprises optical axis make stair-stepping pattern arrangement become concentric circles, at class's face number of every regulation the rank structure of the height of mobile corresponding exponent number amount only with this class's face number, y is taken as arbitrarily even number, d _bWhen being made as the optical path difference of adding for described first light beam, satisfy following formula by the jump between the adjacent described class face in the described figure:

y×0.95×λ1≤d _b≤y×1.05×λ1。

9. objective lens optical system according to claim 8 is characterized in that, described class face number is in 4,5,6 any one, and y is 2.

10. objective lens optical system according to claim 1, it is characterized in that, has the 3rd diffraction structure, the 3rd diffraction structure makes the luminous flux of diffraction light of other any number of times of light flux ratio of 0 time diffraction light of described first light beam all big, make the luminous flux of diffraction light of other any number of times of light flux ratio of 0 time diffraction light of described second light beam all big, make the luminous flux of diffraction light of other any number of times of light flux ratio of r time diffraction light of described the 3rd light beam all big, wherein r be with p identical or different 0 beyond integer.

11. objective lens optical system according to claim 10, it is characterized in that, the information of regeneration carry out to(for) described first optical information recording medium and/or numerical aperture when record, described objective lens optical system are made as NA1, the information of regeneration carry out to(for) described the 3rd optical information recording medium and/or numerical aperture when writing down, described objective lens optical system when being made as NA3, NA1 is bigger than NA3, described first diffraction structure is formed in the zone that is equivalent in the NA3, and described the 3rd diffraction structure is formed on and is equivalent in the outer zone of NA3.

12. objective lens optical system according to claim 10 is characterized in that, described the 3rd diffraction structure is the binary structure of 2 values, d _cWhen being made as a jump by described binary structure, satisfy following formula for the additional optical path difference of described first light beam:

4.8×λ1≤d _c≤5.2×λ1。

13. objective lens optical system according to claim 1, it is characterized in that, the information of regeneration carry out to(for) described second optical information recording medium and/or numerical aperture when record, described objective lens optical system are made as NA2, when numerical aperture the information of regeneration carry out to(for) described the 3rd optical information recording medium and/or record the time, described objective lens optical system is made as NA3, NA2 is bigger than NA3, described first diffraction structure is formed in the zone that is equivalent in the NA3, and described second diffraction structure is formed in the zone that is equivalent in the NA2.

14. objective lens optical system according to claim 13 is characterized in that, described second diffraction structure is formed on and is equivalent in the outer zone of NA3.

15. objective lens optical system according to claim 1, it is characterized in that, when numerical aperture the information of regeneration carry out to(for) described second optical information recording medium and/or record the time, described objective lens optical system is made as NA2, described second diffraction structure is formed on whole of the zone that is equivalent in the NA2, and the diffracting power of described second diffraction structure is for just.

16. objective lens optical system according to claim 1 is characterized in that, described objective lens optical system has phase structure, makes positive integer in that a is got, and b gets the work arbitrarily positive integer littler than a, and c gets the work arbitrarily positive integer littler than b, d ₁Get the optical path difference of work, d by described first light beam of a jump generation of described phase structure ₂Get the optical path difference of work, d by described second light beam of a jump generation of described phase structure ₃When getting the optical path difference of making described the 3rd light beam that a jump by described phase structure produces, various below satisfying:

a×0.95×λ1≤d ₁≤a×1.05×λ1

b×0.95×λ2≤d ₂≤b×1.05×λ2

c×0.95×λ3≤d ₃≤c×1.05×λ3

0.9×d ₁≤d ₂≤1.1×d ₁

0.9×d ₁≤d ₃≤1.1×d ₁。

17. objective lens optical system according to claim 16 is characterized in that, satisfies following various:

a＝10

b＝6

c＝5

350nm≤λ1≤440nm

570nm≤λ2≤670nm

750nm≤λ3≤880nm。

18. objective lens optical system according to claim 16 is characterized in that, and is described with the overlapping setting of same optical surface at objective lens optical system of first diffraction structure and described phase structure.

19. objective lens optical system according to claim 18, it is characterized in that the diffraction light flux of other any number of times of diffraction light flux ratio of u time that the diffraction light flux of other any number of times of diffraction light flux ratio of t time that described phase structure is all big at the diffraction light flux of other any number of times of diffraction light flux ratio of s time that make described first light beam, make described second light beam is all big, make described the 3rd light beam all greatly, to get m be positive integer, get d _aFor during for the additional optical path difference of described first light beam, satisfying following formula by described first diffraction structure:

|(d _a/p)/(d ₁/s)|＝m，

Wherein, s is the integer beyond 0, and t is a integer beyond 0 but different with s, and u is a integer beyond 0 but different with s, t.

20. objective lens optical system according to claim 16 is characterized in that, the cross sectional shape that described phase structure comprises optical axis is stepped.

21. objective lens optical system according to claim 10 is characterized in that, described first diffraction structure and described the 3rd diffraction structure are arranged in the same optical surface of described objective lens optical system.

22. objective lens optical system according to claim 21 is characterized in that, described first diffraction structure and described the 3rd diffraction structure are overlapping.

23. objective lens optical system according to claim 10 is characterized in that, described second diffraction structure and described the 3rd diffraction structure are arranged in the same optical surface of described objective lens optical system.

24. objective lens optical system according to claim 23 is characterized in that, described second diffraction structure and described the 3rd diffraction structure are overlapping.

25. objective lens optical system according to claim 1 is characterized in that, described first diffraction structure is with in described second diffraction structure is arranged on the different optical surface of described objective lens optical system.

26. objective lens optical system according to claim 25 is characterized in that, when optical axis direction is seen described objective lens optical system, described first diffraction structure and described second diffraction structure overlap.

27. objective lens optical system according to claim 25 is characterized in that, when optical axis direction is seen described objective lens optical system, described first diffraction structure and described second diffraction structure do not overlap.

28. objective lens optical system according to claim 1 is characterized in that, described objective lens optical system has lens and dull and stereotyped optical element, and described planar optics element has described first diffraction structure and described second diffraction structure.

29. objective lens optical system according to claim 10, it is characterized in that, described objective lens optical system has lens and dull and stereotyped optical element, and described planar optics element has the described mat woven of fine bamboo strips one diffraction structure, described second diffraction structure and described the 3rd diffraction structure.

30. objective lens optical system according to claim 16 is characterized in that, described objective lens optical system has lens and dull and stereotyped optical element, and described planar optics element has described first diffraction structure, described second diffraction structure and described phase structure.

31. objective lens optical system according to claim 1 is characterized in that,

Described phase structure and described first diffraction structure are overlapping,

It is the shape that stair-stepping pattern arrangement becomes concentric circles that described phase structure has the cross sectional shape that will comprise optical axis,

Described first diffraction structure has: in rank of described stair-stepping figure, the cross sectional shape that will comprise optical axis is the shape that little stair-stepping pattern arrangement becomes concentric circles.

32. objective lens optical system according to claim 31, it is characterized in that, described stair-stepping figure be along with on perpendicular to the direction of optical axis near optical axis, at optical axis direction in the structure that is directed downwards extension towards described objective lens optical system inside, described little stair-stepping figure be along with on perpendicular to the direction of optical axis near optical axis, at optical axis direction in the upwardly extending structure of direction towards described objective lens optical system outside.

33. objective lens optical system according to claim 31, it is characterized in that, be made as the jump of described stair-stepping figure at the jump that dp is made as described little stair-stepping figure, DP, when n being made as the refractive index under first light beam of optical material of the described objective lens optical system that is provided with described stepped and described little stair-stepping figure, various below satisfying:

0.9＜dp×(n-1)/λ1＜1.5

9.8＜DP×(n-1)/λ1＜10.2。

34. objective lens optical system according to claim 33 is characterized in that, dp ₂Be made as the jump of described second diffraction structure, n _xWhen being made as the refractive index under first light beam of optical material of the described objective lens optical system that is provided with described second diffraction structure, satisfy following formula:

1.9＜dp ₂×(n _x-1)/λ1＜2.1。

35. optical take-up apparatus; be used to carry out the record and/or the regeneration of optical information recording medium; have: first light source that penetrates first light beam of first wavelength X 1 be used to have the record of first optical information recording medium of protective seam that thickness is t1 and/or regeneration; ejaculation is used to have the secondary light source of second light beam of second wavelength X 2 of the record of second optical information recording medium of protective seam that thickness is t2 and/or regeneration; ejaculation is used to have the 3rd light source of the 3rd light beam of the wavelength lambda 3 of the record of the 3rd optical information recording medium of protective seam that thickness is t3 and/or regeneration; and objective lens optical system; wherein; t1≤t2; 1.5 * λ 1＜λ 2＜1.7 * λ 1; t2＜t3; 1.9 * λ 1＜λ 3＜2.1 * λ 1

Described objective lens optical system has first diffraction structure and second diffraction structure,

Described first diffraction structure makes the diffraction light flux of other any number of times of diffraction light flux ratio of p time of described first light beam all big, make the diffraction light flux of other any number of times of diffraction light flux ratio of p time of described second light beam all big, make the diffraction light flux of other any number of times of diffraction light flux ratio of p time of described the 3rd light beam all big, wherein p is the integer beyond 0

Described second diffraction structure makes the luminous flux of diffraction light of other any number of times of light flux ratio of 0 time diffraction light of described first light beam all big, make the luminous flux of diffraction light of other any number of times of light flux ratio of q time diffraction light of described second light beam all big, make the luminous flux of diffraction light of other any number of times of light flux ratio of 0 time diffraction light of described the 3rd light beam all big, wherein q is the integer beyond identical or different with p 0.

36. optical information recording/reproducing device; has optical take-up apparatus; this optical take-up apparatus has: first light source that penetrates first light beam of first wavelength X 1 be used to have the record of first optical information recording medium of protective seam that thickness is t1 and/or regeneration; ejaculation is used to have the secondary light source of second light beam of second wavelength X 2 of the record of second optical information recording medium of protective seam that thickness is t2 and/or regeneration; ejaculation is used to have the 3rd light source of the 3rd light beam of the wavelength lambda 3 of the record of the 3rd optical information recording medium of protective seam that thickness is t3 and/or regeneration; and objective lens optical system; wherein; t1≤t2; 1.5 * λ 1＜λ 2＜1.7 * λ 1; t2＜t3; 1.9 * λ 1＜λ 3＜2.1 * λ 1; it is characterized in that

Described objective lens optical system has first diffraction structure and second diffraction structure,

Described first diffraction structure makes the diffraction light flux of other any number of times of diffraction light flux ratio of p time of described first light beam all big, make the diffraction light flux of other any number of times of diffraction light flux ratio of p time of described second light beam all big, make the diffraction light flux of other any number of times of diffraction light flux ratio of p time of described the 3rd light beam all big, wherein p is the integer beyond 0

Described second diffraction structure makes the luminous flux of diffraction light of other any number of times of light flux ratio of 0 time diffraction light of described first light beam all big, make the luminous flux of diffraction light of other any number of times of light flux ratio of q time diffraction light of described second light beam all big, make the luminous flux of diffraction light of other any number of times of light flux ratio of 0 time diffraction light of described the 3rd light beam all big, wherein q is the integer beyond identical or different with p 0.

37. objective lens optical system according to claim 10 is characterized in that,

Described phase structure and described the 3rd diffraction structure are overlapping,

It is the shape that stair-stepping pattern arrangement becomes concentric circles that described phase structure has the cross sectional shape that will comprise optical axis,

Described the 3rd diffraction structure has: in rank of described stair-stepping figure, the cross sectional shape that will comprise optical axis is the shape that little stair-stepping pattern arrangement becomes concentric circles.

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